共查询到18条相似文献,搜索用时 234 毫秒
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《中国舰船研究》2021,(5)
[目的]近年来,液润表面(LIS)作为一种新型的减阻表面被提出。它将传统疏水表面微沟槽中残存的气体替换为润滑油,进而提高了减阻效果的稳定性。为了更全面地认识液润表面,研究润滑油溶解性对滑移长度的影响。[方法]基于格子Boltzmann方法(LBM)伪势模型,对液润表面的滑移现象进行数值模拟,研究润滑油溶解密度和外部剪切率对滑移长度的影响规律。[结果]液润表面可以产生滑移现象,当润滑油完全混溶或极难溶时,滑移长度与组分间分子作用强度有较好的线性关系。[结论]润滑油难溶于水时,组分间作用力越大,减阻效果越好。且滑移长度不显著依赖于剪切率,润滑油的减阻特性与传统超疏水壁面的减阻特性有相似性。 相似文献
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超临界LNG在印刷板式汽化器微细流道内的流动与换热性能数值研究 总被引:1,自引:0,他引:1
以印刷板式汽化器内直径1.5 mm的微细流道为研究对象,应用数值仿真技术手段研究超临界LNG在不同流道弯曲角度的微细流道内的流动与换热特性,重点研究了不同流道弯曲角度对超临界LNG流动换热时的Nu数、表面对流换热系数及压降的影响。研究结果表明:随着流道弯曲角度的增加,超临界LNG出口温度和速度均随之增加,流道弯曲角度为45°时其出口温度较平直流道增加96 K,出口速度约为平直流道出口速度的2.3倍。通过综合分析流道弯曲角度对Nu数、表面传热系数及压降的依变关系发现,超临界LNG在弯曲角度15°的微细流道内具有较优的流动换热特性。 相似文献
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微气泡流的数值模拟及减阻机理分析 总被引:12,自引:1,他引:11
本文采用k-ω湍流模型,进行微气泡流动的数值模拟.在数学模型中,将气泡流作为混合物的流动处理,同时考虑了气泡与水的相对运动.应用该模型,计算了不同气泡直径及喷入速度、不同主流速度下某三维回转体周围微气泡分布及其阻力变化,计算结果与已发表的试验研究的结论相当吻合.对计算结果的分析表明,微气泡减阻的关键是生成足够小的气泡并使之尽量附着在物体表面附近以获得较高的空隙率. 相似文献
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利用铝酸酯偶联剂X-30制备超疏水纳米二氧化硅粒子 总被引:1,自引:0,他引:1
以甲苯为溶剂用自制的廉价铝酸酯偶联剂X-30改性纳米二氧化硅,然后构造一个具有微纳米结构的二氧化硅表面使其达到超疏水效果.用傅里叶红外光谱(FT-IR)、X射线衍射光谱(XRD)、扫描电镜(SEM)、表面水接触角测量(WCA)对改性后的纳米二氧化硅进行分析,并探讨其最佳工艺条件.研究结果表明:该方法得到的纳米二氧化硅表面成功地被偶联剂包覆,其表面水接触角为150.1°,达到超疏水效果. 相似文献
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采用分形方法来研究磨损过程中摩擦副表面三维形貌的变化规律.在环-盘摩擦磨损试验机上进行两因素的全因素试验.利用分阶段换试样的方法获取磨损过程中不同磨损时间后的盘和环表面.采用激光共聚焦显微镜采集盘和环表面的三维形貌,并用具有尺度独立性的分形维数表征磨损表面三维形貌的复杂性和不规则性.结果发现:不同载荷和速度下盘表面三维形貌分形维数的变化规律为先增大,然后维持稳定,最后减小;环表面三维形貌分形维数的变化规律为先减小,然后在小范围内波动,最后再减小.通过与摩擦副表面三维形貌的变化对比发现,盘和环表面分形维数的变化与摩擦副的磨合磨损、稳定磨损和剧烈磨损阶段相对应.研究结果可以用于表面磨损状态识别. 相似文献
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ZHAO Jia-peng DU Xiang-dang SHI Xiu-hua 《船舶与海洋工程学报》2007,6(3):58-61
Many recent studies have confirmed the existence of liquid slip over particular types of solid surfaces, and these so-called super-hydrophobic surfaces have been shown to generate effective liquid slip because of the air trapped between the surface structures. In this paper, based on boundary layer theory, the microscopic structure of the super-hydrophobic surface is analyzed. The liquid slip effect on friction-reduction over super-hydrophobic surfaces under various flow conditions is investigated by experiments with a flume and water tunnel. The experimental results show that the greatest amount of drag-reduction that can be achieved is 8.76% at a low Re. 相似文献
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Engelund弯道环流公式理论性强、国际上应用广泛,但底部边界条件假设不尽合理,致使公式不适用于粗糙床面。修正了底部滑移速度,提出河底横向湍流切应力形式,将两者用于边界条件。据此得到光滑和粗糙床面统一的弯道环流流速公式,改进了Engelund公式。改进公式具有普遍适用性,且计算值与实测资料符合度优于前人公式。 相似文献
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Vortex-induced vibration (VIV) of flexible risers with both internal and external flows has received much attention recently. Hence, VIV dynamics of a fluid-conveying flexible riser subjected to external shear current is investigated. The effect of internal flow velocity and fluid density on VIV response is mainly examined and analyzed. A time domain model is introduced and elaborated. Then the finite element method is adopted to discretize the governing equations. Firstly, the model is validated based on the comparison between the numerical and experimental results. Then the influence of the internal flow velocity and fluid density on VIV dynamics is studied. The results show that multi-frequency response occurs when the flexible riser with various internal flow velocities and densities is subjected to external shear current. Under same shear current velocity, the IL mean deflection is enlarged with the increase of the internal flow velocity and fluid density. In addition, the internal flow velocity and fluid density have an evident effect on the vibrating frequency and the root mean square (RMS) displacement in both in-line (IL) and cross-flow (CF) directions. Moreover, mode and frequency transitions can be observed under different internal flow velocities and fluid densities. 相似文献
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沟槽面减阻效果影响因素及减阻机理的分析 总被引:1,自引:0,他引:1
采用雷诺平均N-S方程和RNG k-ε湍流模型计算V型沟槽面的湍流边界层流动和粘性阻力,研究了沟槽尖峰形状和雷诺数对减阻效果的影响规律,初步分析了沟槽面减阻机理.指出:沟槽尖峰处的圆角半径越小其减阻效果越好,沟槽斜面中下部的壁面应力随着圆角半径的减小而降低,但尖峰处的局部壁面应力会随之增大;来流速度对沟槽减阻率的影响很大,对于一种尺度的V型沟槽,存在着一个具有较好减阻效果的来流速度范围,而沟槽面在沿来流方向上的布置位置对减阻效果的影响非常小;沟槽尺度对减阻效果很剧烈;沟槽尖峰处生成的二次涡是产生减阻效果的根本原因,二次涡的强弱与沟槽减阻率的大小紧密相关. 相似文献
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软体排是航道整治工程中的基础结构,其水力特性直接影响航道整治工程的护滩效果。通过建立水槽模型,研究软体排压载体附近流场结构、回流区长度、近底流速、紊动流场、切应力等水力特性。结果表明,设置软体排压载体后,近底流速和回流区流速减小,上层流速和水流纵向紊动强度增加,近底层的切应力则明显减小。压载体的设置有利于调节近底水流流态、促进泥沙落淤,提高工程边滩守护效果。 相似文献
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《船舶与海洋工程学报》2017,(3)
Experimental investigations have been carried out to study morpho-hydraulic characteristics such as scour geometry and turbulent flow properties around tandem piers in alluvial channels. Experiments were carried out in a plane sand bed with two circular piers of same diameter arranged in tandem manner under no seepage, 10% seepage and 20% seepage conditions. Downward seepage minimizes the scour depth around piers and restrains the development of scour depth with time. Strong reversal flow is found near the bed at upstream of piers and near free surface at downstream of piers where velocity and Reynolds shear stress are found to be negative which reduce in magnitude with downward seepage. The flow is more critical within the gap between two piers where velocity is lesser near free surface and gradually increasing towards bed. Quadrant analysis shows that contribution of each event to the total Reynolds shear stress increases with downward seepage. Sedimentation effect prevails within the scour hole whereas outside the scour hole erosive forces become more dominant. Reduced reversal flow at upstream of pier because of downward seepage results in decreasing higher order moments and turbulent kinetic energy. At downstream of piers, secondary currents are dominant due to wake vortices. Strouhal number decreases in case of seepage runs than no seepage condition. 相似文献